Virtual electrodes for high-density electrode arrays

ABSTRACT

The present embodiments are directed to implantable electrode arrays having virtual electrodes. The virtual electrodes may improve the resolution of the implantable electrode array without the burden of corresponding complexity of electronic circuitry and wiring. In a particular embodiment, a virtual electrode may include one or more passive elements to help steer current to a specific location between the active electrodes. For example, a passive element may be a metalized layer on a substrate that is adjacent to, but not directly connected to an active electrode. In certain embodiments, an active electrode may be directly coupled to a power source via a conductive connection. Beneficially, the passive elements may help to increase the overall resolution of the implantable array by providing additional stimulation points without requiring additional wiring or driver circuitry for the passive elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure is a division of co-pending U.S. patentapplication Ser. No. 13/440,925, entitled VIRTUAL ELECTRODES FOR HIGHDENSITY ELECTRODE ARRAYS, filed Apr. 5, 2012, the disclosure of which ishereby incorporated herein by reference.

Cross-Reference to Related Applications

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/516,818, filed Apr. 8, 2011 and entitled, “VIRTUAL ELECTRODES,”the entire contents of which are specifically incorporated herein byreference without disclaimer.

GOVERNMENT INTEREST

This invention was made with government support under DE-SC0004116awarded by Department of Energy. The government has certain rights inthe invention.

TECHNICAL FIELD

This invention relates to bio-stimulation devices and more particularlyrelates to virtual electrodes for implantable bio-stimulation devices.

BACKGROUND

Electrical stimulator devices are used to stimulate various types oforganic tissue. For example, electronics may be interfaced with thenervous system of a human body through use of neurostimulators. Aneurostimulator is a device that may be implanted into human tissue, andprovides stimulation to neurons through electrical pulses. For suchreasons, neurostimulators may be referred to as implanted pulsegenerators (IPGs).

A typical neurostimulator includes one or more electrodes. Someneurostimulators include arrays of electrodes configured in implantabledevices. For example, FIG. 1 illustrates a typical system 100 forneurostimulation. The system 100 includes an implantable electrode array102 which may be implanted in organic tissue 106. For example, theimplantable electrode array 102 may be implanted in a human brain ornear optical or auditory nerves. The system 100 also includes acontroller 104 coupled to the implantable electrode array 102. Theelectrode controller 104 is often located outside of the body. Incertain systems, however, the electrode controller 104 may also beimplantable.

FIG. 2 illustrates one configuration of a electrode array 102. Asillustrated, the electrode array 102 includes a plurality of electrodes202 a-d, and a current return 204. A dielectric backing 107 mechanicallysupports the array and helps directing the charge injection into thetissue. The electrode array 102 may be implanted so the electrodes arein contact with organic tissue 106. In most prior systems, the currentreturn 204 is placed in a region relatively distal from the electrodearray 102. Each of the electrodes is coupled to a power source whichinjects charge on the electrodes 202 a-d. The charge is injected throughthe organic tissue 106 to the current return 204, thus stimulating theorganic tissue 106 between the electrodes 202 a-d and the current return204. Typically, only the portions of organic tissue 106 directlyproximate each of the electrodes 202 a-d are stimulated.

In order to increase the stimulation resolution of an electrode array102, additional electrodes 202 may be included in the electrode array102. For example, in the case of a retinal prosthesis, the electrodearray 102 may originally have included nine electrodes 202. In an effortto increase resolution, the electrode array 102 could eventually includesixty-four electrodes 202 and then two hundred electrodes 202 or more inlater versions.

In prior stimulator systems, as the number of electrodes increases, forthe same size device, each electrode has to be smaller. This causes thecurrent density at the vicinity of the stimulating electrodes to growaccordingly, to a point in which further miniaturization may lead tocurrent density magnitudes that can damage the tissue. Additionally anadditional wire and an additional driver circuit are typically requiredfor each electrode, and the wire needs to have a large enough section toallow the appropriate amount of current to flow. These wires make theimplant bulkier, mechanically stiffer, and in general harder to conformto delicate anatomical features.

SUMMARY

The present embodiments are directed to implantable electrode arrayshaving virtual electrodes. The virtual electrodes may improve theresolution of the implantable electrode array without the burden ofcorresponding additional wiring and complexity of electronic circuitry.In a particular embodiment, a virtual electrode may include one or morepassive elements. For example, a passive element may be a metalizedlayer on a substrate that is adjacent to, but not directly connected toan active electrode. In certain embodiments, an active electrode may bedirectly coupled to a power source via a conductive connection.Beneficially, the passive elements may help to increase the overallresolution of the implantable array by providing additional stimulationpoints without requiring additional wiring or driver circuitry for thepassive elements.

In the proposed scheme, the excitation waveform used in the electrodeshas higher frequency components than what the body can react to. Theneural cells being stimulated respond then to an averaged stimulus overtime.

Embodiments of an apparatus for stimulating biological tissue aredescribed. In one embodiment, the apparatus includes a first activeelectrode configured to receive a current from a current source andinjecting it into organic tissue. The apparatus may also include asecond active electrode configured to return current emitted by thefirst active electrode to ground. Additionally, the apparatus mayinclude a region defining a virtual electrode disposed between the firstactive electrode and the second active electrode.

In further embodiments, a portion of the current emitted by the firstactive electrode is collected in the region defining the virtualelectrode. Additionally, the time-average current density present in theregion defining the virtual electrode is sufficient to stimulatebiological tissue in proximate to the region defining the virtualelectrode. The region defining the virtual electrode may include one ormore passive elements. The passive elements may include a conductivelayer disposed on a substrate in the region defining the virtualelectrode. Additionally, an electrical insulation barrier may bedisposed between the first and second active elements and the one ormore passive elements. In one embodiment, the one or more passiveelements are shaped in a pattern of a cross, a center point of the crossbeing disposed at a center point of the region defining the virtualelectrode. In another embodiment, a majority portion of the regiondefining the virtual electrode comprises the one or more passiveelements.

In such embodiments, the apparatus may include a plurality of activeelectrodes arranged in an array. Additionally, the apparatus may includea plurality of regions defining virtual electrodes, the virtualelectrodes positioned between the plurality of active electrodes in thearray. This is accomplished by means of tiling the same electrodepattern over a larger region.

Embodiments of systems for stimulating biological tissue are alsopresented. In one embodiment, the system includes an implantablebio-stimulator device. The implantable bio-stimulator device may have afirst active electrode configured to inject current into tissue from acurrent source, a second active electrode configured to sink the currentinjected by the first active electrode, and a region defining a virtualelectrode disposed between the first active electrode and the secondactive electrode. Additionally, the system may include a current sourcecoupled to the implantable bio-stimulator device and configured tosupply current to the first and second active electrodes in theimplantable bio-stimulator array. In a further embodiment, the systemincludes an electrode controller coupled to the implantablebio-stimulator device, and configured to control operation of theimplantable bio-stimulator device.

The system may also include one or more conductors coupling the firstand second active electrodes to the electrode controller. The electrodecontroller may also include one or more driver circuits coupled to thefirst and second active electrodes, the driver circuit configured tosupply current from the current source to the first and second activeelectrodes according to a timing sequence.

Methods of stimulating biological tissue are also presented. In oneembodiment a method includes providing a stimulating current to a firstactive electrode in an implantable bio-stimulator device, and collectingreturn current from a second active electrode in the implantablebio-stimulator device. The first active electrode and the second activeelectrode may be arranged in an array configuration with one or moreregions defining virtual electrodes disposed adjacent to the firstactive electrode and the second active electrode.

Additionally, the method may include providing the stimulatingelectrical charge in a pulse current pulse having finite pulse duration,the pulse duration sufficient to allow a portion of the electricalcharge injected by the first electrode to accumulate in a regiondefining a virtual electrode. The region defining a virtual electrodemay have one or more passive elements configured to steer the injectedelectrical charges to a predetermined position within the regiondefining the virtual electrode.

Additionally, the methods may include providing a plurality currentwaveforms to a plurality of active electrodes in an implantable array ofbio-stimulator electrodes comprising both active electrodes and virtualelectrodes, wherein the duration, timing, waveform, and firing sequencesof the injected current is sufficient to generate a stimulation currentin the virtual electrodes. A sequence of the waveforms may be applied topreselected active electrodes in the array of electrodes according to apredetermined pattern.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating a system forbiostimulation according to the prior art;

FIG. 2 is a perspective view diagram illustrating one embodiment of animplantable electrode array according to the prior art;

FIG. 3 is a logical diagram illustrating an embodiment of a stimulationcurrent path;

FIG. 4 is a logical diagram illustrating another embodiment of astimulation current path;

FIG. 5 is a schematic diagram illustrating one embodiment of animplantable electrode array having a virtual electrode;

FIG. 6 is a graphical diagram illustrating a comparison oftime-accumulated normalized current density magnitude across an activeelectrode and a virtual electrode in an embodiment that does not includea passive element;

FIG. 7 is a schematic diagram illustrating one embodiment of anelectrode array having passive elements;

FIG. 8A is a graphical diagram illustrating a pattern oftime-accumulated normalized current density at 10 μm from the embodimentof an implantable sensor array shown in FIG. 7;

FIG. 8B is a graphical diagram illustrating a pattern oftime-accumulated normalized current density at 30 μm from the embodimentof an implantable sensor array shown in FIG. 7;

FIG. 8C is a graphical diagram illustrating a pattern oftime-accumulated normalized current density at 50 μm from the embodimentof an implantable sensor array shown in FIG. 7;

FIG. 9 is a graphical diagram illustrating a comparison oftime-accumulated normalized current density magnitude across an activeelectrode and a virtual electrode in the embodiment of an implantablesensor array shown in FIG. 7;

FIG. 10 is a schematic diagram illustrating another embodiment of anelectrode array having passive elements;

FIG. 11A is a graphical diagram illustrating a pattern oftime-accumulated normalized current density at 10 μm from the embodimentof an implantable sensor array shown in FIG. 10;

FIG. 11B is a graphical diagram illustrating a pattern oftime-accumulated normalized current density at 30 μm from the embodimentof an implantable sensor array shown in FIG. 10;

FIG. 11C is a graphical diagram illustrating a pattern oftime-accumulated normalized current density at 50 μm from the embodimentof an implantable sensor array shown in FIG. 10;

FIG. 12 is a graphical diagram illustrating a comparison oftime-accumulated normalized current density magnitude across an activeelectrode and a virtual electrode in the embodiment of an implantablesensor array shown in FIG. 10;

FIG. 13 is a schematic diagram illustrating another embodiment of anelectrode array having passive elements;

FIG. 14 is a graphical diagram illustrating a comparison oftime-accumulated normalized current density magnitude across an activeelectrode and a virtual electrode in the embodiment of an implantablesensor array shown in FIG. 13;

FIG. 15 is a schematic flowchart diagram illustrating one embodiment ofa method of using an implantable electrode array having a virtualelement.

DETAILED DESCRIPTION

Various features and advantageous details are explained more fully withreference to the non-limiting embodiments that are illustrated in theaccompanying drawings and detailed in the following description.Descriptions of well known starting materials, processing techniques,components, and equipment are omitted so as not to unnecessarily obscurethe invention in detail. It should be understood, however, that thedetailed description and the specific examples, while indicatingembodiments of the invention, are given by way of illustration only, andnot by way of limitation. Various substitutions, modifications,additions, and/or rearrangements within the spirit and/or scope of theunderlying inventive concept will become apparent to those skilled inthe art from this disclosure.

FIGS. 3A-3B are logical diagrams illustrating embodiments of astimulation current path. In FIG. 3, the external current return 204 iseliminated. For example, in the implantable electrode array 102 of FIG.3, the electrodes 202 a-d may be configured such that electrode 202 a iscoupled to a current source and electrode 202 b is configured as acurrent return for current emitted by electrode 202 a. Thus, a flow ofcurrent between electrode 202 a and electrode 202 b may be established.As described in the paragraphs to follow, a configuration in which afirst electrode (e.g., 202 a) is a current source and a second electrode(e.g., 202 b) is a current return may be beneficial for controllingpositioning of current density in tissue surrounding the electrodes(e.g., 202 a-b) in the electrode array. FIG. 4 illustrates a secondembodiment, wherein a diagonal current path is established between afirst electrode (e.g., 202 a) and a second electrode (e.g., 202 c).

There are several distinctions that can be drawn from a comparison ofthe present embodiments with the prior art system of FIG. 2. Forexample, in the present embodiments, the active electrodes 202 a-d arealso configurable as current returns, where as in the prior art thecurrent return 204 is not included as one of the elements of theelectrode array 102. Indeed, it is the configurations in which thecurrent is drawn between the electrodes in the array that helpsfacilitate distribution of charge to the virtual electrode discussedbelow with respect to FIG. 5. As illustrated in various embodimentsherein, an current injection electrode (e.g., 102 a) may situated in acoplanar orientation with the current return electrode (e.g., 102 c).Indeed, because the current injection electrode and the current returnelectrode are part of a common electrode array 102, they may be formedon a common substrate.

FIG. 5 is a schematic diagram illustrating one embodiment of animplantable electrode array 102 having a virtual electrode 502. In oneembodiment, the implantable electrode array 102 may include a pluralityof electrodes 202 a-d that are actively powered. The virtual electrode502 may be passively powered by charge injection for the activelypowered electrode 202 a-d. For example, a current may be injected on afirst electrode 202 a for 0.1 μs and a second electrode 202 c that issituated diagonally across from the first electrode 202 a may beconfigured as a current collector for the current injected on the firstelectrode 202 a. In such an embodiment, charge may flow through thevirtual electrode region 502. In such an embodiment, charge may berapidly injected from neighboring electrodes 202 a-d using predeterminedspatial and temporal patterns which are configured to increase thetime-average amount of charge present in the area of the virtualelectrode 502.

FIG. 6 is a graphical diagram illustrating a comparison of accumulatednormalized current density magnitude across an active electrode 202 a-dand a virtual electrode 502 in an embodiment that does not include apassive element. As illustrated, there is some increase in the currentdensity in the region corresponding to the virtual electrode, but thecurrent density is still far lower than the current density at thecenter of the active electrodes 202 a-d.

FIG. 7 is a schematic diagram illustrating another embodiment of anelectrode array 102 having one or more passive elements 702 comprisingthe virtual electrode 502. In this embodiment, the passive elements 702may include a plurality of conductive arms positioned adjacent to theelectrodes 202 a-d. The passive elements 702 do not actually touch oneanother. The passive elements 702 may be formed of a bio-compatibleconductive material, such as gold, platinum, or other suitableconductive materials. In one embodiment, the passive elements 702 atleast partially insulated from the electrodes 202 a-d. Thus, in oneembodiment, current density may accumulated on the passive electrodes702, thereby creating a region of relatively higher charge density atthe center point of the virtual electrode 502.

One benefit of including the passive elements 702 is that the passiveelements 702 provide a low-resistance path between the current injectionelectrode (e.g., 102 a) and the current return electrode (e.g., 102 c).Thus, the charge will be more likely to follow a path along the passiveelements 702 from the current injection electrode to the current returnelectrode. Accordingly, if the passive elements 702 are positioned in aregion defining a virtual electrode 502, then the virtual electrode 502will exhibit a higher current density than would be likely without thepassive elements 702. FIGS. 9A-C illustrate this as well. Variousgeometries may be used to generate a variety of current densitycharacteristics in the virtual electrode 502.

FIG. 8A is a graphical diagram illustrating a pattern of accumulatednormalized current density at 10 μm from the embodiment of animplantable sensor array 102 shown in FIG. 7. In this embodiment, agreater level of current density can be seen as the relatively lightportions of FIG. 7. Although it appears that the greatest currentdensity corresponds to the position of the active elements 202 a-d,there does appear to be a higher current density concentration at thecenter of the virtual electrode 502 which is indicated by the lightershaded portions in the middle of FIG. 8A. FIG. 8B is a graphical diagramillustrating a pattern of accumulated normalized current density at 30μm from the embodiment of an implantable sensor array 102 and FIG. 8C isa graphical diagram illustrating a pattern of accumulated normalizedcurrent density at 50 μm from the implantable sensor array 102.

FIG. 9 is a graphical diagram illustrating a comparison of accumulatednormalized current density magnitude across an active electrode 202 a-dand a virtual electrode 502 in the embodiment of an implantable sensorarray 102 shown in FIG. 7. In this embodiment, a significant increase inthe current density over the embodiment of FIG. 5 which did not includea passive element. Thus, it appears that in at least this “cross”configuration, the passive element facilitates collection of greatercharge density at the center of the virtual electrode 502.

FIG. 10 is a schematic diagram illustrating another embodiment of anelectrode array 102 having passive elements 702. In this embodiment, thepassive elements are configured to take up the majority of the area ofthe virtual electrode 502, leaving only a cross-shaped gap between thepassive elements. Further, in this embodiment, the passive elements 702are configured to match the contour of the active electrode 202 a-d,thereby gaining greater electromagnetic coupling with the activeelectrodes 202 a-d.

FIG. 11A is a graphical diagram illustrating a pattern of accumulatednormalized current density at 10 μm from the embodiment of animplantable sensor array 102 shown in FIG. 10. In this embodiment, itcan be seen by the lighter cross-shaped portion in the center of thevirtual electrode 502 that a relatively high level of current density isachievable than with the previously discussed embodiments. FIG. 11B is agraphical diagram illustrating a pattern of accumulated normalizedcurrent density at 30 μm and FIG. 11C is a graphical diagramillustrating a pattern of accumulated normalized current density at 50μm. These show the highest current density at 50 μm.

FIG. 12 is a graphical diagram illustrating a comparison of accumulatednormalized current density magnitude across an active electrode 202 a-dand a virtual electrode 502 in the embodiment of an implantable sensorarray 102 shown in FIG. 10. As can be seen from this graph, the currentdensity achievable in the virtual electrode 502 is at or above the samelevel that is achievable in the active electrodes 202 a-d. Thus, bytuning the size and geometry of the passive element, a variety ofdifferent current density levels and patters are achievable in thevirtual electrode 502.

One of ordinary skill in the art will recognize other geometries for thepassive elements 702 which may be suitable for various applications. Forexample, triangle shapes, star shapes, and other similar geometries maybe used. In each case, one of ordinary skill in the art will appreciatethat the current density in the region defining the virtual electrode502 may be tuned by adjustment of the geometry including shape and sizeof the one or more passive elements 702.

FIG. 13 is a schematic diagram illustrating another embodiment of anelectrode array 102 having passive elements 702. In the embodiment ofFIG. 13, a region of the passive elements 702 adjacent to the activeelements 202 a-d is shaped to match a contour of the active elements 202a-d. In such an embodiment, a greater degree of electromagnetic couplingbetween the active elements 202 a-d and the passive elements 702 may beachieved. For example, FIG. 14 is a graphical diagram illustrating acomparison of accumulated normalized current density magnitude across anactive electrode and a virtual electrode in the embodiment of animplantable sensor array shown in FIG. 13.

FIG. 15 is a schematic flowchart diagram illustrating one embodiment ofa method 1500 of using an implantable electrode array 102 having avirtual element 502. In one embodiment, a method 1500 includes providing1504 a stimulating current to a first active electrode (e.g., 202 a) inan implantable bio-stimulator device 102, and collecting 1506 returncurrent from a second active electrode (e.g., 202 c) in the implantablebio-stimulator device. The first active electrode 202 a and the secondactive electrode 202 c may be arranged in an array configuration 102with one or more regions defining virtual electrodes 502 disposedadjacent to the first active electrode 202 a and the second activeelectrode 202 c.

Additionally, the method 1500 may include providing the stimulatingcurrent in a pulse current pulse having finite pulse duration, the pulseduration sufficient to allow a significant portion of the currentemitted by the first electrode 202 a to reach into a region defining avirtual electrode 502. The region defining a virtual electrode 502 mayhave one or more passive elements 702 configured to direct the currentto a predetermined position within the region defining the virtualelectrode 502.

Additionally, the methods 1500 may include providing a plurality ofcurrent pulses to a plurality of active electrodes 202 a-d in animplantable array 102 of bio-stimulator electrodes comprising bothactive electrodes 202 a-d and virtual electrodes 502, wherein a durationof the pulses is sufficient to generate a stimulation current in thevirtual electrodes 502 as illustrated in FIGS. 6, 9, 12 and 14. A timingand/or sequence of the pulses may be applied to preselected 1502 activeelectrodes in the array 102 of electrodes according to a predeterminedpattern.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method of stimulating biological tissue, themethod comprising: providing a stimulating current to a first activeelectrode in an implantable bio-stimulator device; and collecting returncurrent from a second active electrode in the implantable bio-stimulatordevice.
 2. The method of claim 1, wherein the first active electrode andthe second active electrode are arranged in an array configuration withone or more regions defining a virtual electrode disposed adjacent tothe first active electrode and the second active electrode, and whereinthe virtual electrode positioned such that the virtual electrodereceives at least a portion of the current transferred between the firstactive electrode and the second active electrode.
 3. The method of claim1, further comprising providing the stimulating current in a pulsecurrent pulse having finite pulse duration, the pulse durationsufficient to allow a portion of the current emitted by the firstelectrode to accumulate in a region defining a virtual electrode.
 4. Themethod of claim 3, wherein the region defining a pulse durationcomprises one or more passive elements configured to direct the currentto a predetermined position within the region defining the virtualelectrode.
 5. The method of claim 4, comprising providing a pluralitycurrent pulses to a plurality of active electrodes in an implantablearray of bio-stimulator electrodes comprising both active electrodes andvirtual electrodes, wherein a duration of the pulses is sufficient togenerate a stimulation current in the virtual electrodes.
 6. The methodof claim 5, wherein a sequence of the pulses are applied to preselectedactive electrodes in the array of electrodes according to apredetermined pattern.